Methods and Systems for In-Situ Extraction of Bitumen

ABSTRACT

A method for carrying out in-situ bitumen extraction can include a step of forming one or more vertical freeze walls within or around a deposit of bituminous material and establishing a laterally confined deposit of bituminous material; a step of injecting a solvent within the laterally confined deposit of bituminous material; a step of withdrawing a mixture of dissolved bitumen and solvent from within the laterally confined deposit of bituminous material; a step of injecting water within the laterally confined deposit of bituminous material; and a step of withdrawing a mixture of solvent and water from within the laterally confined deposit of bituminous material.

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/511,921, filed Jul. 26, 2011, and U.S. Provisional PatentApplication No. 61/525,590, filed Aug. 19, 2011. Each application isincorporated herein by reference in its entirety.

BACKGROUND

Deposits of bituminous material can be found throughout the world.including in the United States and Canada. Depending on the depth of thebituminous material, various methods can be used to extract bitumen frombituminous deposits. When the bituminous material is located relativelyclose to the surface, surface mining can be used to remove thebituminous material from the ground. However, deeper deposits ofbituminous material cannot be economically obtained through surfacemining. Accordingly, methods involving the use of well bores drilledinto the bituminous deposits have been developed.

One such method for obtaining deeper deposits of bituminous material isthe Steam Assisted Gravity Drainage (SAGD) method. The SAGD methodgenerally includes injecting steam into the bituminous deposit to warmthe bituminous material and make it flowable. Once the viscosity of thebituminous material is sufficiently lowered, the bituminous material canflow downwardly to a horizontal production well that is positioned belowthe horizontal well used to inject steam into the deposit. While theSAGD method can be relatively effective in extracting bituminousmaterial from bitumen deposits, other methods that do not require theuse of water and that provide better bitumen extraction rates aredesired.

The use of solvents to extract bitumen from mined oil sands or the likeis considered an effective method for separating bitumen from othercomponents of the oil sands material. The solvent is generally used todissolve the bitumen, after which the bitumen-loaded solvent isseparated from the sand, clay, and other components of the oil sands.The injection of solvent into a deposit of oil sands to dissolve thebitumen would appear to be an effective means for extracting bitumenfrom a bituminous deposit, but several problems are associated withsolvent injection into the ground that have prevented the method frombeing feasible.

One primary problem with injecting solvent into the oil sands deposit isthat it has been difficult or impossible to recover a sufficient amountof the injected solvent to make the process economical. For example, insome instances, only 25% of the solvent injected into the deposit can berecovered. The cost of having to replenish large amounts of solvent tocontinue the process generally makes the process uneconomical.

An additional problem with injecting solvent into the oil sands depositsrelates to the environmental concerns of injecting potentially hazardoussolvent material into the ground without any effective way of recoveringthe solvent or preventing the solvent from migrating to a locationoutside of the oil sands deposit. For example, if the oil sands depositis near an aquifer, then concerns arise regarding the flow of solventout of the oils sands deposit and into the aquifer, where potential wellwater would be contaminated.

SUMMARY

The foregoing and other features, utilities and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

In some embodiments, a method of in-situ bitumen extraction isdisclosed, the method including a step of forming one or more verticalfreeze walls within or around a deposit of bituminous material andestablishing a laterally confined deposit of bituminous material; a stepof injecting a solvent within the laterally confined deposit ofbituminous material; a step of withdrawing a mixture of dissolvedbitumen and solvent from within the laterally confined deposit ofbituminous material; a step of injecting water within the laterallyconfined deposit of bituminous material; and a step of withdrawing amixture of solvent and water from within the laterally confined depositof bituminous material.

In some embodiments, a system for in-situ bitumen extraction isdisclosed, the system including a plurality of vertical freeze wallbores formed in a deposit of bituminous material and aligned in ageometric pattern; a refrigerant source in fluid communication with theplurality of vertical freeze wall bores; a plurality of verticalinjection bores formed win the deposit of bituminous material andlocated within the geometric pattern of the plurality of freeze walls; awater source in fluid communication with the plurality of verticalinjection bores; a solvent source in fluid communication with theplurality of vertical injection bores; and a plurality of verticalproduction wells formed in the deposit of bituminous material andlocated within the geometric pattern of the plurality of freeze walls.

The foregoing and other features and advantages of the presentapplication will become more apparent from the following detailed,description, which proceeds with reference to the accompanying figures.In this regard, it is to be understood that the scope of the inventionis to be determined by the claims as issued and not by whether givensubject includes any or all features or aspects noted in this Summary oraddresses any issues noted in the Background.

BRIEF DESCRIPTION OF THE DRAWING

The preferred and other embodiments are disclosed in association withthe accompanying drawings in which:

FIG. 1 is flow chart of embodiments of an in-situ bitumen extractionmethod described herein;

FIG. 2 is an aerial view of a configuration of well bores formed in adeposit of bituminous material in accordance with some embodimentsdescribed herein;

FIG. 3 is an aerial view of a configuration of well bores formed in adeposit of bituminous material, including a two loop refrigerantcirculation system according to some embodiments described herein;

FIG. 4 is a cross-sectional view of a bituminous deposit having avertical injection well and a vertical production well formed therein inaccordance with some embodiments described herein;

FIG. 5 is a cross-sectional view of a bituminous deposit having ahorizontal injection well and a horizontal production well formedtherein in accordance with some embodiments described herein; and

FIG. 6 is a cross-sectional view of a composite injection well accordingto some embodiments described herein.

DETAILED DESCRIPTION

With reference to FIG. 1, some embodiments of a method of in-situextraction of bitumen generally include a step 100 of forming one ormore vertical freeze walls within or around a deposit of bituminousmaterial and establishing a laterally confined deposit of bituminousmaterial, a step 110 of injecting a solvent within the laterallyconfined deposit of bituminous material, a step 120 of withdrawing amixture of dissolved bitumen and solvent from within the laterallyconfined deposit of bituminous material, a step 130 of injecting waterwithin the laterally confined deposit of bituminous material, and a step140 of withdrawing a mixture of solvent and water from within thelaterally confined deposit of bituminous material. Such embodiments cansuccessfully confine material injected into the bituminous depositwithin a prescribed area. Similarly, mixtures of dissolved bitumen andsolvent created by injecting material into the bituminous deposit aremaintained within the area defined by the freeze walls. Accordingly,contamination of, for example, underground water sources can bemitigated or prevented and recovery of dissolved bitumen can be enhancedby providing barriers around the bitumen deposit being subjected to thebitumen extraction processes.

In step 100, one or more vertical freeze walls are formed within oraround a deposit of bituminous material. The vertical freeze wallsformed within or around the deposit of bituminous material form aboundary around all or a portion of the deposit of bituminous materialand establish a laterally confined deposit of bituminous material. Anobjective of step 100 is to provide vertical boundaries that willprevent material injected into the deposit of bituminous material andmixture of materials formed within the bituminous deposit from travelingoutside of the laterally confined area, thus alleviating environmentalconcerns of in-situ bitumen extraction and making collection ofdissolved bitumen easier.

The deposit of bituminous material in which the vertical freeze wallsare formed in step 100 can be any suitable deposit of bituminousmaterial. Suitable deposits of bituminous material include tar sands oroil sands formations, such as those located in the Athabasca region ofCanada. In some embodiments, the deposit of bituminous material is adeposit or a portion of a deposit that is located at a depth that is toodeep for surface mining but too shallow for traditional in-situ bitumenextraction methods such as steam assisted gravity drainage (SAGD). Insome embodiments, the deposit of bituminous material is located at adepth of from between 250 feet and 1,500 feet below the surface.

The one or more freeze walls formed in the deposit of bituminousmaterial can be any type of freeze wall capable of slowing or preventingthe movement of fluids through the freeze wall. The freeze walls aretypically made from water that is naturally present in the ground in aliquid form. By freezing this water, a barrier of ice is created in theground. Freeze walls can be formed in deposits of bituminous materialbecause bituminous material (such as oil sands deposits) typicallyincludes a water content.

Any manner of forming the one or more freeze walls known to those ofordinary skill in the art can be used in the embodiments of this method.In an exemplary method, a series of interconnected vertical well boresare constructed within or around the deposit of bituminous material, anda refrigerant is circulated through the vertical well bores until thewater in the ground proximate the vertical well bores freezes. Therefrigerant can be continuously circulated through the vertical wellbores to ensure the water remains frozen and the freeze walls remainintact. Any suitable refrigerant can be used, such as brine or ammonia.In some embodiments, the refrigerant is circulated within the well boresfor a period of from 6 weeks to 16 weeks in order to establish thefreeze walls.

The arrangement and spacing of the vertical well bores within or aroundthe deposit of bituminous material can be any suitable arrangement forproviding freeze walls. In some embodiments, the vertical well bores arespaced close enough together that the water in the area between twoadjacent vertical well bores can be frozen to create a vertical freezewall. In some embodiments, the well bores are spaced apart approximately2 to 6 meters from one another.

The dimensions of the well bores can vary based on the specificapplication but are typically selected to ensure that a suitable amountof refrigerant passes through the well bores to freeze the Water in thesurrounding ground. In some embodiments, the well bores have a diameterin the range of from 3 to 15 inches. The depth of the well bores can bedependent on a variety of factors. In some embodiments, the depth of thewell bores is selected based on the depth of the deposit of bituminousmaterial and/or the depth of any bed rock or other geological formationthat might be located beneath the deposit of bituminous material. A bedrock or other geological formation below the deposit of bituminousmaterial can serve as a lower horizontal boundary for the deposit ofbituminous material, so it can be beneficial to extend the well boresdown to abut a rock formation or the like. Generally speaking, the wellbores will have a depth of from 100 to 1,500 feet.

In some embodiments, the vertical well bores are arranged in a closedgeometric pattern (when looking down at the vertical well bores fromabove) to thereby create vertical freeze walls that enclose a deposit ofbituminous material. Any suitable closed geometric shape can be used.With reference to FIG. 2, the vertical well bores 200 are arranged in arectangular shape, with each side of the rectangle including severalwell bores 200. The well bores 200 are spaced close enough to freeze thearea 210 between each well bore 200 and ultimately form a series ofvertical freeze walls arranged in a rectangular shape and enclosing adeposit of bituminous material 220.

The well bores used to form the freeze walls are generally constructedby drilling vertical holes into the deposit of bituminous material andproviding piping within the drilled holes. The piping can be anysuitable type of piping, but is typically of a type that is impermeableto fluids and has good heat transfer for allowing the refrigerant tofreeze the water proximate the piping. The piping may also havestructural additions to improve heat transfer, such as a plurality offins extending out from the piping. As noted above, the piping providedin the drilled holes can be interconnected with piping in adjacentdrilled holes such that the refrigerant can circulate throughout theplurality of well bores.

In some embodiments, the well bores constructed for establishing freezewalls in the deposit of bituminous material can include a two loopsystem of interconnected well bores. The two loop system allows forrefrigerant to be supplied into the interconnected well bores in a firstloop and for refrigerant to be removed from the interconnected wellbores in a second loop. With reference to FIG. 3, the two loop system300 provides a first loop 310 where refrigerant is introduced into thesystem to flow through the well bores 350 and create and/or maintainfreeze walls. The first loop 310 extends around the closed geometricarrangement of well bores 350 and is in fluid communication 315 witheach of the well bores 350 such that refrigerant introduced into thefirst loop 310 can travel to each of the well bores 350 and providerefrigerant into the well bores 350. The two loop system also includes asecond loop 320. Like first loop 310, second loop 320 extends around theclosed geometric arrangement of well bores 350 and is in fluidcommunication 325 with each of the well bores 350. Second loop 320receives refrigerant that has flowed through the well bores 350 andprovides a path 360 for the refrigerant to leave the system 300. In someembodiments, the first loop 310 will be in fluid communication at abottom end of each well bore 350 and the second loop 320 will be influid communication with the top end of each well bore 350 such that newrefrigerant is introduced into each well bore 350 at the bottom via thefirst loop 310 and then exits the well bore 350 at the top via thesecond loop 320. The opposite arrangement can also be used. The two loopsystem 300 provides a manner for fresh refrigerant to be introduced intothe system and for used refrigerant to be taken out of the system, whereit can be reconditioned and reinjected back into the well bores 350.

Well bores as described above are not the only mechanism that can beused to create the freeze walls in step 110. In some embodiments, freezewalls can be formed using thermosyphons. Thermosyphons generally includea fully enclosed system having a low temperature fluid (such as liquidCO₂, or ammonia) circulating inside. Natural convection allows theliquid to pick up heat from the bed rock at the bottom of the closedsystem below and convert to a vapor. The vapor rises to the top of thesystem, where cooling occurs (such as wind cooling via radiators) toconvert the vapor back to liquid. The cooled liquid drains back to thebottom of the system, and the process repeats.

As noted above, bed rock or other geological formations can be used toserve as a lower horizontal barrier of the confined deposit ofbituminous material. However, natural harriers may not always beavailable. Accordingly, in some embodiments, steps can also be taken toform a horizontal freeze wall that will serve as a barrier thatvertically confines the deposit of bituminous material. Generallyspeaking, such a horizontal freeze wall will extend up to or beyond thevertical freeze walls laterally confining the deposit of bituminousmaterial. It can also be preferable to have the horizontal freeze wallabut the bottom end of the vertical freeze walls. In this manner, thematerial injected into the confined deposit of bituminous material willbe prevented from leaving the confined area in both a lateral directionand in a downward direction.

Any suitable manner of forming horizontal freeze walls can be used. Insome embodiments, the manner of forming the horizontal freeze wall issimilar or identical to the manner in which the vertical freeze wallsare used. For example, directional drilling techniques can be used toform a plurality of horizontal well bores through which refrigerant canflow in order to freeze the water in the ground between adjacenthorizontal well bores.

In step 100, the vertical freeze walls formed serve to laterally confinea deposit of bituminous material. When bed rock (or other geologicalformation) or a horizontal freeze wall are used in conjunction with thevertical freeze walls, a “bath tub” configuration is provided that iscapable of retaining liquid material within the confined “bath tub”area. Accordingly, when solvents are injected into the confined area ofbituminous material, the “bath tub” configuration mitigates oreliminates concerns related to injected solvent drilling out of the areaundergoing bitumen extraction and into, for example, underground watersources. Similarly, the “bath tub” configuration helps to keep dissolvedbitumen within a confined area, which helps make withdrawing dissolvedbitumen from the deposit of bituminous material more effective andefficient.

In step 110, a solvent is injected into the laterally confined depositof bituminous material. The injected solvent is injected to dissolvebitumen and create a diluted bitumen (or “dilbit”) phase within thedeposit. Once dissolved, the mixture of bitumen and solvent can bewithdrawn from the deposit to thereby extract bitumen.

The solvent used in step 110 may include a hydrocarbon solvent. Anyhydrocarbon solvent or mixture of hydrocarbon solvents that is capableof dissolving bitumen can be used. The hydrocarbon solvent or mixture ofhydrocarbon solvents can be economical and relatively easy to handle andstore. The hydrocarbon solvent or mixture of hydrocarbon solvents mayalso be generally compatible with refinery operations.

In some embodiments, the solvent is paraffinic. Any paraffinic solventsuitable for use in dissolving bitumen can be used. In some embodiments,the paraffinic solvent is pentane. Other suitable paraffinic solventsinclude, but are not limited to, ethane, butane, hexane and heptane

It should be appreciated that the paraffinic solvent need not be 100%paraffinic solvent. Instead, the paraffinic solvent may include amixture of paraffinic and non-paraffinic compounds. For example, thesolvent can include greater than zero to about 100 wt % paraffiniccompounds, such as approximately 10 wt % to 100 wt % paraffiniccompounds, or approximately 20 wt % to 100 wt % paraffinic compounds.

In some embodiments, a portion or all of the solvent is derived frombitumen recovered by the in-situ bitumen extraction process describedherein. The bitumen extracted by the process described herein can besubjected to distillation processing to separate a light end portion ofthe bitumen that is suitable for use as a solvent in the processdescribed herein. In some embodiments, the light end portion of therecovered bitumen is a fraction of the bitumen having a boiling pointtemperature in the range of up to 225° C.

Any distillation methods capable of separating fractions of bitumenmaterial known to those of ordinary skill in the art can be used,including the use of atmospheric or vacuum distillation towers. In someembodiments, a make-up solvent, such as any of the above discussedsolvents, can be mixed with the light end portion of the bitumen inorder to provide a suitable amount of solvent for the process. Obtaininga portion or all of the solvent from the bitumen recovered by thein-situ bitumen extraction process described herein can be useful inthat the process can become essentially self-sustainable. Additionally,use of solvent derived from the recovered bitumen can reduce oreliminate environmental concerns associated with using non-indigenous orcommercial solvents.

In some embodiments, the solvent can include a mixture of water andperoxide. Suitable peroxides for use as the solvent include those whichproduce oxygen micro-bubbles upon being mixed with hydrocarbon liquidsor solids. Exemplary peroxides suitable for use as solvent includehydrogen peroxide, peroxide salts, and any compounds capable ofproducing hydrogen peroxide on decomposition in water (e.g., sodiumpercarbonate). Peroxide can be useful as an extraction solvent at leastin part due to its ability to alter surface conditions, such as reducinginterfacial tension between hydrocarbon material, water, and inorganicmaterial of the bituminous deposit (including rocks). Reducedinterfacial tension can, for example, help release bitumen from withinpores in the bituminous deposit. Exothermic heat release associated withthe use of the peroxides can also assist in removal of bitumen due tothe heat release decreasing the viscosity of the bitumen. The decreasedviscosity improves flowability and drainage and ultimately makes thematerial easier to recover.

The oxygen micro-bubbles formed from the mixing of peroxide andhydrocarbon material can also be useful in stripping hydrocarbonmaterial such as bitumen from inorganic material (such as sand) in thebituminous deposit. It is believed that the oil stripped from the sandwill form a film on the oxygen micro-bubbles. The stripped bitumenmaterial can then be recovered in the same manner as other free bitumenin the bituminous deposit, i.e., by injecting additional wash materials(e.g., water) into the bituminous deposit to mix with the oxygenmicro-bubbles and carry the stripped bitumen out of the deposit viaproduction wells. The continuous injection of a solvent. including waterand peroxide will continue to produce the oxygen micro-bubbles havingbitumen films within the deposit of bituminous material and provideadditional free bitumen for recovery from subsequent in situ washcycles.

In some embodiments, the mixture of peroxide and water injected into thedeposit as a solvent is from 10 wt % to 60 wt % (including from 3 wt %to 5 wt %) peroxide.

In some embodiments, the desired amount of solvent is injected into thedeposit of bituminous material and is then allowed to stay in thedeposit of bituminous material for a period of time before productionwells are used to remove the mixture of solvent and bitumen. In someembodiments, the solvent is held in the deposit of bituminous materialfor a period of from 1 day to 1 month.

The amount of solvent injected into the laterally confined deposit ofbituminous material can be any suitable amount of solvent needed fordissolving bitumen. In some embodiments, the amount of solvent injectedinto the deposit of bituminous material will depend on the quality ofthe deposit of bituminous material (i.e., the bitumen content of thebituminous material). Larger bitumen contents can require larger amountsof solvent to ensure as much bitumen as possible is dissolved into adilbit phase. The amount of solvent injected into the deposit ofbituminous material can also vary on the size of the area beingsubjected to bitumen extraction. In some embodiments, the amount ofsolvent injected into the deposit ranges from 0.5:1 to 5:1.

In some embodiments, the desired amount of solvent is injected into thedeposit of bituminous material and is then allowed to stay in thedeposit of bituminous material for a period of time before productionwells are used to remove any dilbit formed. Holding the solvent in thedeposit of bituminous material allows for the solvent to migrate to alarger area and have sufficient time to dissolve the bitumen. In someembodiments, the solvent is held in the deposit of bituminous materialfor a period of from 1 day to 1 month.

Any suitable technique for injecting solvent into the laterally confineddeposit of bituminous material can be used in step 110. In someembodiments, one or more injection wells are formed in the laterallyconfined area, which allows for solvent to flow down and into thebituminous material bound by the freeze walls. Once the solvent isinjected into the confined deposit of bituminous material, the solventworks to dissolve the bitumen and create a dilbit phase within thedeposit of bituminous material. The injection wells can be paired withproduction wells capable of drawing the dilbit phase out of the depositof bituminous material and up to the surface.

The injection wells can be any type of injection wells suitable forinjecting solvent into a deposit of bituminous material, and can beconstructed by any suitable technique used by those or ordinary skill inthe art to construct injection wells. Similarly, production wells usedto draw fluid material out of the deposit of bituminous material (suchas dilbit) can be any suitable type of production well and can beconstructed by any suitable technique for constructing production wells.In some embodiments, the injection wells and productions wells aresimilar enough that injection wells can be transformed into productionwells with minimal modifications.

The dimensions of the production wells and injection wells can be anysuitable dimensions needed to carry out the in-situ bitumen extraction.The length of the injection wells and the production wells willgenerally be equal to or slightly shorter than the depth of the depositof bituminous material. The diameter of the injection wells andproduction wells can vary, and in some embodiments, range from 6 to 12inches.

With reference to FIG. 4, the injection wells formed in the laterallyconfined area can be vertical injection wells 410 that have a pluralityof injection ports 415 located along the height of the injection well410 for injecting solvent into the deposit of bituminous material 400 atvarious depths. The injection ports 415 are capable of injecting solventinto the deposit of bituminous material 400, and in some cases willgenerally inject solvent into the bituminous deposit 400 at a directionperpendicular to the vertical injection well 410. The vertical injectionwells 410 can be paired with vertical production wells 430 that arespaced apart a distance from the injection wells 410. In this manner,the vertical production wells can collect the mixture of solvent anddissolved bitumen produced upon injecting solvent into the deposit ofbituminous material 400.

With reference to FIG. 5, the injection wells formed in the laterallyconfined area can also be a series of horizontal injection wells 510.The horizontal injection wells 510 generally have an L-shapedconfiguration that includes a vertical portion 510 a and a horizontalportion 510 b. Solvent travels down into the deposit of bituminousmaterial 500 via the vertical portion 510 a and is injected into thedeposit of bituminous material 500 via the horizontal portion 510 b. Insome embodiments, a plurality of injection ports 515 are located alongthe length of the horizontal portion 510 b of the horizontal injectionwell 510 such that solvent is injected into the deposit of bituminousmaterial 500 at various locations along the length of the horizontalportion 510 b of the horizontal injection well 510. In some embodiments,the injection ports 515 are oriented to inject solvent upwardly into thebituminous deposit 500. Horizontal production wells 530 can also beincluded to withdraw the dilbit formed upon the injection of solventinto the deposit of bituminous material 500 via the horizontal injectionwell 510. In some embodiments, the horizontal production wells 530 havea vertical portion 530 a and horizontal portion 530 b. The horizontalportion 530 b can be located parallel to and below the horizontalportion 510 b of the horizontal injection well 510. The dilbit formedabove the horizontal portion 510 b flows downwardly where it collectedin the horizontal portion 530 b of the horizontal production well 530.The collected dilbit is then transported up the vertical portion 530 aof the horizontal production well 530 to the surface.

The injection wells and production wells are formed within the area ofbituminous material confined by the freeze walls established in step100. The arrangement of the plurality of injection wells and productionwells is generally not limited and can include any arrangement that willprovide for multiple solvent injection locations and multiple dilbitproduction locations. Generally speaking, the injection wells andproduction wells are located close enough to one another that theproduction wells can receive the dilbit created by injecting solventinto the deposit of bituminous material via the injection wells. In someembodiments, a production well is located from 50 to 100 feet from aninjection well.

In some embodiments, more injection wells than production wells will beprovided within the deposit of bituminous material confined by thefreeze walls, such as from 2 to 6 injection wells per production well.The arrangement of injection wells and production wells can includevarious geometric shapes and patterns. One exemplary arrangementinvolves a hexagonal matrix of production wells surrounding an injectionwell located in the middle of the hexagon.

In some embodiments where vertical injection wells and production wellsare used, the arrangement of injection wells and production wells can bea straight line arrangement of injection wells and a straight linearrangement of production wells parallel to the injection wells andspaced apart a suitable distance. The straight lines of injection wellsand production wells can be located relatively close to one of thefreeze walls making up the boundary of the confined deposit ofbituminous material, and can also be oriented in parallel to that freezewall. Thus, for example, in a rectangular shaped confined deposit ofbituminous material, a straight line of injection wells can be locatednext to and in parallel with a freeze wall, while a straight line ofproduction wells can be located next to and in parallel with thestraight line of injection wells, and further away from the freeze wallthen the injection wells. The injection ports on the injection wells canbe pointed in a direction towards the production wells (i.e., away fromthe freeze wall) to extract bitumen from the area closest to the freezewall. Once this area has been sufficiently treated, the injection wellscan be decommissioned, the production wells can be converted toinjection wells (including positioning injection ports in a directionaway from the freeze wall), and a new straight line of production wellscan be formed further into the confined area and in parallel with thestraight line of injection wells. The space between the new injectionwells and the new production wells can be treated for a sufficientperiod of time, after which the above described process of convertingproduction wells into injection wells and forming new production wellsis repeated. This cycle can be repeated until the entire length of therectangular confined area is subjected to bitumen extraction. Such asystem can be referred to as a “line drive” process of extractingbitumen.

In some embodiments, the injection of solvent is preceded and/orfollowed by an agitation step. Agitation prior to solvent injection canhelp top open the formation such that solvent can better penetrate thedeposit of bituminous material. Agitation after solvent injection canpromote mixing between the solvent and the bituminous material. Anysuitable manner of causing agitation within the bituminous deposit canbe used. In some embodiments, the agitation step includes a gasinjection or gas pulsation step. In both gas injection and gaspulsation, the introduction of the gas into the deposit leads toimproved mixing between the solvent and the bituminous material, whichin turn leads to more bitumen dissolving in the solvent. When used priorto solvent injection, both the gas injection and gas pulsation can leadto opening of passageways within the deposit to allow for improvedpenetration of the solvent in the bituminous material.

The gas injection or gas pulsation step can be carried out using theinjection wells described in greater detail above. For example, in gasinjection, the gas is injected into the deposit via the same injectionwells used to inject the solvent into the bituminous deposit. Any gassuitable for use in agitating the solvent in the bituminous deposit canbe used. In some embodiments, the gas is unreactive to the materials inthe bituminous deposit such that the injection of the gas leads toprimarily the mechanical agitation of the solvent and not to thereaction between the gas and the solvent or materials in the bituminousdeposit. Exemplary passes that can be used include but are not limitedto natural gas, steam, nitrogen, air, and carbon dioxide.

In some embodiments, the gas is preferably injected into the bituminousdeposit at relatively high volumes to ensure agitation. In someembodiments, the gas is injected into the bituminous deposit at a rateof 0.20 to 1.45 BCFD depending on the geologic conditions and oilproduction rate, or, in some embodiments, from 130 BOPD to 600 BOPD perMMCFD of gas injected. When gas pulsation is used, the frequency of thegas pulsation can be between 2 and 10 Hz. The injection of solvent intothe bituminous deposit can be carried out in several cycles. In someembodiments, the agitation step is carried out after every cycle ofinjecting solvent into the bituminous deposit.

In step 120, a mixture of solvent and dissolved bitumen produced frominjecting solvent into the deposit of bituminous material in step 110 iswithdrawn from within the laterally confined deposit of bituminousmaterial. Any suitable manner of withdrawing the dilbit from within thedeposit of bituminous material can be used to carry out step 120. Asdiscussed in greater detail above, in some embodiments the dilbit iswithdrawn from within the deposit of bituminous material usingproduction wells that are located proximate the injection wells.Production wells can be operated for extended periods of time, such asup to 9 months, to ensure that the vast majority of the dilbit producedin step 110 is withdrawn from the deposit. In some embodiments, theproduction wells are operated until 90% of the dilbit produced in step110 is removed. Step 120 is usually performed after step 110 iscompleted, but is some embodiments, step 120 can be commenced prior tostep 110 being completed.

The fluid material withdrawn from within the deposit of bituminousmaterial in step 120 generally includes solvent and dissolved bitumen.Other materials that can be present in the fluid material include water,and organic and inorganic solids. Generally speaking, the fluid materialwithdrawn in step 120 includes from 40 to 75% solvent, from 25 to 60%bitumen, from 0 to 5% water, and less than 2% other materials. The rateof withdrawing the fluid material is generally not limited, and in someembodiments, the fluid is withdrawn from within the deposit ofbituminous material via the production wells at a rate of from about5,000 to 25,000 bbls/day.

Once the mixture of dissolved bitumen and solvent is brought to thesurface in step 120, various separation steps can take place to separatethe bitumen, solvent, and water. Any suitable separation unit or seriesof separation units can be used to separate the bitumen, solvent, andwater, such as distillation towers. Once separated, the bitumen can befurther processed, such as by being subjected to upgrading to produceuseful lighter hydrocarbons. The recovered solvent can be reused in thebitumen extraction process, such as by reusing the solvent in step 110.

Steps 110 and 120 described above can be repeated several. Performingmultiple cycles of injecting solvent and withdrawing a mixture ofsolvent and bitumen can help to improve the overall amount of bitumenrecovered using the methods described herein.

In some embodiments, step 120 will not be capable of withdrawing all ofthe solvent injected into the deposit of bituminous material in step110. For example, from 10 to 50% of the solvent injected into thedeposit of bituminous material may remain in the deposit after thecompletion of step 120. For environmental and economical reasons,additional steps should be taken to attempt to remove solvent from thedeposit of bituminous material.

In steps 130 and 140, water is injected into the bituminous material todisplace the residual solvent towards the production wells, where thesolvent and water may then be withdrawn from the laterally confineddeposit of bituminous material. The water injected into the deposit canbe in the form of steam or as liquid water.

The manner of injecting water is similar or identical to the manner inwhich the solvent is injected into the deposit of bituminous material.The same injection wells used for injecting solvent can be used toinject water. The amount of water injected into the laterally confineddeposit of bituminous material can be any suitable amount of waterneeded for removing the solvent. In some embodiments, the amount ofwater injected into the deposit of bituminous material will depend onthe amount of residual solvent remaining in the deposit. The amount ofwater injected into the deposit of bituminous material can also varybased on the size of the area being subjected to bitumen extraction. Insome embodiments, the amount of water injected into the deposit rangesfrom 3:1 to 10:1 on a water:bitumen ratio.

In some embodiments, the desired amount of water is injected into thedeposit of bituminous material and is then allowed to stay in thedeposit of bituminous material for a period of time before productionwells are used to remove the mixture of water and solvent. In someembodiments, the water is held in the deposit of bituminous material fora period of from 1 day to 1 month.

The manner of withdrawing a mixture of water and solvent from within thedeposit if bituminous material is similar or identical to the manner inwhich the mixture of solvent and dissolved bitumen is withdrawn from thedeposit of bituminous material. The same production wells used towithdraw dilbit and solvent from the deposit can be used to withdraw amixture of water and solvent from the deposit.

The fluid material withdrawn from within the deposit of bituminousmaterial in step 140 generally includes water and solvent. Othermaterials that can be present in the fluid material include water,bitumen, and organic and inorganic solids. Generally speaking, the fluidmaterial withdrawn in step 140 includes from 40 to 90% water, from 60 to95%, from 2 to 10% bitumen, and less than 2% other materials. Theconstituency of the fluid withdrawn in step 140 can change over time asthe injected water reaches the well head. The rate of withdrawing thefluid material is generally not limited, and in some embodiments, thefluid is withdrawn from within the deposit of bituminous material viathe production wells at a rate of from about 500 to 2,000 bbls/day perwell head (by gravity drainage).

Once the mixture of water and solvent is brought to the surface in step140, various separation steps can take place to separate the water fromthe solvent. Any suitable separation unit or series of separation unitscan be used to separate the water from the solvent. Once separated, thesolvent can be reused in the extraction process.

Any water left in the deposit of bituminous material can remain in thedeposit, as the water is generally not considered an environmentalconcern. In some embodiments, 5 to 50% of the water injected into thedeposit in step 130 will remain in the deposit.

The above described method can be performed one or more times on aconfined deposit of bituminous material. Similarly, any one step orpairs of steps (e.g. step 110 and 120) can be repeated multiple timesbefore moving on to the next step of the method. Repeating certain stepsor pairs of steps may help to increase the bitumen extractionefficiency.

Once a confined deposit of bituminous material has been subjected to theabove-described in-situ bitumen extraction process, the same process canbe carried out on adjacent deposits of bituminous material. In someembodiments, one or more freeze walls established for carrying out thein-situ bitumen extraction process on a first deposit of bituminousmaterial can be re-used when confining an adjoining deposit ofbituminous material. For example, when a confined deposit of bituminousmaterial has a square shape, three of the freeze walls can bedecommissioned while a fourth wall can be used as the first wall of anew confined deposit of bituminous material located next to the firstdeposit.

Additional pretreatment steps can also be carried out prior to or duringthe method described above. For example, any of a variety of fracturingsteps or method to increase porosity can be carried out prior to any ofthe solvent injection steps in an attempt to create more passageways forsolvent and other materials to pass through.

Additionally, hot water or sloppy steam can be injected into the depositof bituminous material prior to or during the injection of the solventin an effort to soften the oil sands and the bitumen component or createchannels for the subsequently injected solvent to pass through. In someembodiments, the injection wells can be adapted to allow for thesimultaneous injection of water and solvent through the same injectionwells. The injection wells can be “composite” injection wells thatinclude multiple passage ways within the same general piping. Withreference to FIG. 6, a composite injection well 600 can include aco-annular inner passage 610 and a co-annular outer passage 620, withthe inner passage 610 having injection ports 615 that extend through theouter passage to the exterior of the injection well 600. In this manner,steam or water can travel down the inner passage 610 of the injectionwell 600 and be injected into the deposit at the same time that solventpasses down the outer passage 620 of the injection well 600 and isinjected into the deposit through standard injection ports 625 in fluidcommunication with the outer passage 620.

The majority of the system used to carry out the in-situ bitumenextraction methods described herein is discussed above, including thevertical freeze walls, the optional horizontal freeze wall, theplurality of injection bores, and the plurality of production wells.Also discussed above are the separation units that can be provided,including the separator for separating dilbit into bitumen and solvent,a separator for separating a mixture of solvent and water, anddistillation units for producing solvent from recovered bitumen.

Additional components that can be part of the system include arefrigerant source, a solvent source, and a water source. Each sourcecan include any type of supply vessel that is capable of supplying thedesired fluid needed for the method. The supply vessels may also includerecycle inputs for receiving fluid material that is recovered from theprocess and sent back into the system. The refrigerant source is influid communication with the interconnected well bores used to establishthe freeze walls and, when a two loop system as described above is used,can include a recycle input for receiving refrigerant that has passedthrough the two loop system back into the refrigerant source for storageand further use. The solvent and water sources can be in fluidcommunication with the outer and inner passage of a composite injectionwell, respectively.

Several advantages can be realized by using the methods and systemsdescribed herein. Specifically, the use of a single solvent where thesolvent is paraffinic can provide numerous advantages over other solventbitumen extraction techniques, including those techniques using morethan one type of solvent. Firstly, the use of paraffinic solvent canincrease the throughput of the method by a factor of 2 or greater.Improved throughput can be realized due to the use of the lighterparaffinic solvent that is capable of solvating the bitumen materialfaster than heavier solvents and results in reduced viscosity dilbit,which can be recovered from the solids easier. The paraffinic solventcan also advantageously precipitate asphaltenes, further eliminating theheavy viscosity component. In some instances, the paraffinic solventcauses the asphaltenes to precipitate into the solids, and morespecifically onto the finer clays. The precipitated asphaltenes arecaptured by finer clays while the dilbit passes through and out of thebitumen material for successful bitumen extraction. The precipitation ofasphaltene can also be beneficial by allowing for the upgrading ofbitumen extracted in the dilbit using conventional upgrading processingequipment (i.e., specialized upgrading equipment capable of handlingasphaltenes as well as bitumen is not required).

The systems and methods that use a single solvent instead of twodifferent types of solvents can also be advantageous from a capitalexpenditure (CAPEX) perspective. Single solvent systems typically onlyrequire a single distillation unit for the separation and recovery ofthe single solvent. Single solvent systems, including single solventsystems using a paraffinic solvent, also tend to require smallerdistillation units as compared to when heavier solvents are used.Operating expenditures (OPEX) are also reduced when using a singlesolvent system versus a two solvent system. For example, lower heatingduty is required for removing a single, relatively light, solvent fromthe tailings. Finally, environmental advantages can result from thesingle solvent system. Carbon dioxide emissions and fugitive solventloses can be reduced when a single solvent system is used in lieu of asystem that uses two different types of solvents.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various other changes in the form anddetails may be made without departing from the spirit and scope of theinvention.

A presently preferred embodiment of the present invention and many ofits improvements have been described with a degree of particularity. Itshould be understood that this description has been made by way ofexample, and that the invention is defined by the scope of the followingclaims.

1. A method of in-situ bitumen extraction comprising: forming one ormore vertical freeze walls within or around a deposit of bituminousmaterial and establishing a laterally confined deposit of bituminousmaterial; injecting a solvent within the laterally confined deposit ofbituminous material; and withdrawing a mixture of dissolved bitumen andsolvent from within the laterally confined deposit of bituminousmaterial.
 2. The method as recited in claim 1, further comprising:injecting water within the laterally confined deposit of bituminousmaterial; and withdrawing a mixture of solvent and water from within thelaterally confined deposit of bituminous material.
 3. The method asrecited in claim 1, wherein the solvent comprises a paraffinic solvent.4. The method as recited in claim 1, wherein the solvent comprisespentante.
 5. The method as recited in claim 1, wherein the methodfurther comprises forming one or more horizontal freeze walls within thedeposit of bituminous material and vertically confining the laterallyconfined deposit of bituminous material.
 6. The method as recited inclaim 1, wherein the one or more vertical freeze walls abut animpervious geological material located below the deposit of bituminousmaterial.
 7. The method as recited in claim 1, wherein forming one ormore vertical freeze walls within or around the deposit of bituminousmaterial comprises: drilling a plurality of spaced apart vertical boreswithin or around the deposit of bituminous material; and circulating arefrigerant through the vertical bores.
 8. The method as recited inclaim 1, wherein injecting the solvent within the laterally confineddeposit of bituminous material comprises: drilling one or more verticalinjection bores within the laterally confined deposit of bituminousmaterial; and injecting the solvent within the laterally confineddeposit of bituminous material through the one or more verticalinjection bores.
 9. The method as recited in claim 8, whereinwithdrawing the mixture of dissolved bitumen and solvent from within thelaterally confined deposit of bituminous material comprises: drillingone or more vertical production bores within the laterally confineddeposit of bituminous material; and withdrawing the mixture of dissolvedbitumen and solvent from the laterally confined deposit of bituminousmaterial through the one or more vertical production bores.
 10. Themethod as recited in claim 9, wherein: the one or more verticalinjection bores are arranged in a straight line; the one or morevertical production bores are arranged in a straight line parallel toand spaced a distance away from the straight line of vertical injectionbores; and the solvent is injected into the laterally confined depositof bituminous material in a direction towards the straight line of oneor more vertical production bores.
 11. The method as recited in claim 1,further comprising: separating the mixture of dissolved bitumen andsolvent withdrawn from within the laterally confined deposit ofbituminous material into a bitumen stream and a solvent stream; andreusing the solvent stream in the step of injecting solvent within thelaterally confined deposit of bituminous material.
 12. The method asrecited in claim 1, wherein the solvent comprises a mixture of water anda peroxide.
 13. The method as recited in claim 12, wherein the mixturecomprises from 10 wt % to 60 wt % peroxide.
 14. The method as recited inclaim 12, wherein the peroxide is hydrogen peroxide.
 15. The method asrecited in claim 1, further comprising agitating the deposit ofbituminous material prior to injecting the solvent within the laterallyconfined deposit of bituminous material.
 16. A system for in-situbitumen extraction comprising: a plurality of vertical freeze wall boresformed in a deposit of bituminous material and aligned in a geometricpattern; a refrigerant source in fluid communication with the pluralityof vertical freeze wall bores; a plurality of vertical injection boresformed win the deposit of bituminous material and located within thegeometric pattern of the plurality of freeze walls; a solvent source influid communication with the plurality of vertical injection bores; anda plurality of vertical production wells formed in the deposit ofbituminous material and located within the geometric pattern of theplurality of freeze walls.
 17. The system as recited in claim 16,further comprising: a bitumen-solvent separator in fluid communicationwith the plurality of vertical production wells.
 18. The system asrecited in claim 16, wherein the plurality of vertical freeze wall boresare in fluid communication with one another.
 19. The system as recitedin claim 16, further comprising a water source in fluid communicationwith the plurality of vertical injection bores.
 20. The system asrecited in claim 19, wherein the plurality of vertical injection boreseach comprises: an inner passage; a co-annular outer passage separatedfrom the inner passage by a partition; a plurality of inner passageinjection ports extending from the inner passage to the exterior of thevertical injection bore; and a plurality of outer passage injectionports extending to the exterior of the vertical injection bore.
 21. Thesystem as recited in claim 20, wherein the inner passage is in fluidcommunication with only the water source and the outer passage is influid communication with only the solvent source.